The cochlea encodes sound pressures varying over six orders of magnitude by collective operation of functionally diverse spiral ganglion neurons (SGNs). The mechanisms enabling this functional diversity remain elusive. Here, we asked whether the sound intensity information, contained in the receptor potential of the presynaptic inner hair cell (IHC), is fractionated via heterogeneous synapses. We studied the transfer function of individual IHC synapses by combining patch‐clamp recordings with dual‐color Rhod‐FF and iGluSnFR imaging of presynaptic Ca²⁺ signals and glutamate release. Synapses differed in the voltage dependence of release: Those residing at the IHC' pillar side activated at more hyperpolarized potentials and typically showed tight control of release by few Ca²⁺ channels. We conclude that heterogeneity of voltage dependence and release site coupling of Ca²⁺ channels among the synapses varies synaptic transfer within individual IHCs and, thereby, likely contributes to the functional diversity of SGNs. The mechanism reported here might serve sensory cells and neurons more generally to diversify signaling even in close‐by synapses.

中文翻译：

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感觉细胞通过改变活性区之间的 Ca2+ 流入释放耦合来使其输出多样化

耳蜗通过功能多样的螺旋神经节神经元 (SGN) 的集体操作对超过六个数量级的声压进行编码。实现这种功能多样性的机制仍然难以捉摸。在这里，我们询问了包含在突触前内毛细胞 (IHC) 的受体电位中的声音强度信息是否通过异质突触分离。我们通过将膜片钳记录与突触前 Ca ²⁺信号和谷氨酸释放的双色 Rhod-FF 和 iGluSnFR 成像相结合，研究了单个 IHC 突触的传递函数。突触在释放的电压依赖性方面有所不同：那些位于 IHC' 支柱侧的突触在更多的超极化电位下被激活，并且通常表现出对少量 Ca ²⁺的释放的严格控制渠道。我们得出的结论是，突触中 Ca ²⁺通道的电压依赖性和释放位点耦合的异质性改变了单个 IHC 内的突触转移，因此，可能有助于 SGN 的功能多样性。这里报道的机制可能更普遍地服务于感觉细胞和神经元，即使在附近的突触中也可以使信号多样化。